I still have my iPhone 4, the first iPhone I had owned. Original battery, but had to replace the screen after I accidentally smashed it with a motorcycle part

. I had the , 5, and 5s, but sold both, continuing to keep this phone. They were okay, but felt far too fragile as compared to the solid feel of this device.
I do have a 6 now, but keep my 4 for iTunes Radio, and other music service via BT in my car and home. It's the main reason I Regret getting a 128gb phone, as I still use the 4 for lots of my media. Since most of my friends have iMessage, Facebook, snapchat, and other open services, I can also still use it to keep in touch with people.
I am bummed that it can't support iOS 8, handoff, continuity, and many of the features in it. Quite honestly if it did, it would remain tethered to the 6, and continue to be my primary phone. I still love the size, and the screen is still bright, clear, and big enough for me.